Molten metal is often dispensed from a bottom discharge pouring and holding reservoir, sometimes referred to as either a tundish or simply a box, into a mold. The tundish is usually kept supplied with molten metal from a ladle. The purity of the metal being discharged from the tundish is important to successfully cast clean metal into the mold. More particularly, the poured metal should be free of slag that forms on the surface of molten metal and also free of bubbles that are sometimes created and entrained in the metal during the pouring process. If the output flow of molten metal from the ladle entrains any slag or any other unwanted inclusion, the quality of the cast metal is degraded. A major contributor to this degradation is the occurrence of vortexing, in the form of whirlpools, created during the pouring operation as a result of Coriolis forces on the flowing metal.
If slag is drawn by a vortex into the stream of molten metal being poured into a tundish or pouring box, it can easily become trapped in the end product. Further, if the stream of molten metal being poured into the mold is spiraling when it exits the bottom nozzle of the reservoir, the stream may become hollow and enlarged so as to expose much of its lateral surface to the atmosphere. If this exposure occurs, the metal may be reoxidized which, in turn, results in a significant loss of quality in the cast product. Products of reoxidation sometimes get trapped in the solidified cast metal and are generally referred to as dirt.
The danger of slag contamination is almost always present because, as metal is melted, a slag is formed on the surface of the molten metal. However, so long as the slag remains on the top surface, it does not present a problem for successful casting. Unfortunately, and typically, when pouring a batch of steel, slag begins to be vortexed into the output flow of the molten metal from the ladle into the tundish and will undesirably find its way into the mold. The presence, or even the danger of such slag being present in the tundish, commonly causes the pouring process to be terminated. For these situations, as much as two to four percent of the metal may still be left in a ladle, and this amount is treated as scrap to be recycled by being remelted. Remelting of this metal results in an additional, undesired cost. It is thus desired to reduce the vortexing of slag from the ladle into the tundish, especially to reduce the need to remelt these large quantities of metal, so as to decrease costs.
The drawbacks of vortexing are present in both continuous casting and ingot pouring operations. In continuous casting, the molten metal continuously flows out of the orifice of a nozzle and onto a mold to form a continuous shape, such as a steel billet, bloom, slab or strip. In non-continuous casting, the flow of molten metal is stopped after an ingot mold is filled, and then re-started when a new ingot mold is in place.
For continuous casting, it is known that undesired vortexing and spiraling may be reduced by the placement of flutes in the orifice of the nozzle (metering nozzle), located in the bottom portion of the tundish, that feeds the molten metal to the mold. Antivortexing devices are also used with ladles which supply the tundish or ingot mold at the outflow or collector nozzle. Antivortexing devices in the collector nozzle help prevent spiraling of the metal stream leaving the nozzle, but have little effect in preventing vortexing in the ladle itself. It is therefore desired to provide additional antivortexing means upstream from the collector nozzle so as to further reduce the drawbacks caused by vortexing in the ladle.
For ingot casting, it is known to use nozzles having a central opening in which are disposed flutes to improve the quality of the stream flowing out of the nozzle so as to eliminate the vortexing and spiraling effects previously discussed. The quantity and rate of the flow out of the nozzle is controlled by a metering device, such as a stopper rod or slide gate.
Internal flutes have also been used with nozzles having a circular, triangular, or square central bore. Typically, after a heat is poured, the nozzle is rinsed with oxygen to free it of any unwanted residue. Unfortunately, casting and rinsing contributes to the deterioration of the flutes and limits the operational life of the flutes associated with the nozzles to about three to four heats. Normally, nozzles without fluted arrangements handle between eight to twelve heats before their replacement is necessary. The removal of a fluted inner nozzle from a metering assembly after every three or four heats is impractical and very time-consuming, especially when compared to a non-fluted nozzle that does not require replacement until eight to twelve heats have been poured. It is therefore desired to provide fluted nozzles within metering assemblies which are easy to replace, and at the same time still reduce undesired vortexing.
Casting equipment already in use in existing pouring operations suffers from the drawbacks of vortexing and spiraling. The replacement of existing equipment to correct for undesired vortexing and spiraling would involve a considerable expense and would also consume extensive time.
Accordingly, it is one object of the present invention to provide means easily placed into existing pouring equipment which reduces disadvantageous vortexing and spiraling so as to advantageously and conveniently yield higher quality cast metal.
It is a further object of the present invention to provide a pouring ladle for continuous casting equipment upstream from the tundish which has a fluted nozzle feeding the tundish so as to further inhibit any vortexing or spiraling that would otherwise add impurities or bubbles into molten metal or would otherwise allow for reoxidation of the poured metal, all of which contribute to degrading the quality of the end product being cast.
It is another object of the present invention to provide an antivortexing device that is suitable for a tundish so as to inhibit any vortexing or spiralling that would add impurities or bubbles into a molten metal mold or would otherwise allow for reoxidation of the poured metal.
It is another object of the present invention to provide a nozzle assembly having a fluted portion that not only reduces vortexing and spiraling conditions but also allows for the convenient replacement of the fluted portion.
Other objects and advantages of the present invention will become apparent to those skilled in the art with reference to the attached drawings and description of the invention which hereinafter follows.